One, two! One, two! And through and through
The vorpal blade went snicker-snack!
He left it dead, and with its head
He went galumphing back.
Closeszcash/pasta_curves#42.
It was only present to enable an FFT implementation in `halo2_proofs`
that is generic over fields and groups, but we can replace it with an
equivalent trait in `halo2_proofs` that can have a blanket impl.
It is only used internally by the table-based square root impl, and we
should probably refactor this further, but for now it can live in the
sqrt extension trait.
- `ff::PrimeField::{from_repr, to_repr}` are direct replacements for
`FieldExt::{from_bytes, to_bytes}`.
- `FieldExt::{read, write}` were added for reading and writing `halo2`
proofs, but `halo2::transcript` now handles this internally.
We can use the `ff::PrimeField::root_of_unity` method everywhere we
currently use this associated constant. If there is a more general
need for accessing this as an associated constant, we should consider
that for `ff::PrimeField`.
They already implement CofactorGroup (trivially, with the prime-order
subgroup being Self); this just enables Pallas and Vesta to be used in
cofactor-aware protocols that also want to leverage the affine point
representation.
